I. Technical Field
The present invention relates to plate glass used as a substrate material or a cover glass member to be mounted on an image display portion or an image input portion of various kinds of portable information terminals typified by a mobile phone and a PDAandanelectronic appliance typifiedbya liquid crystal display, and a method of manufacturing the plate glass.
II. Description of the Related Art
In recent years, as recognized in the progress of a digital technology involving all the industrial fields and the like, the information industry has been remarkably developed, and the prosperity thereof is presenting animated appearance in the same way as in the textile industry, steel industry, shipbuilding industry, or the like. Along with this, the technical innovation regarding various kinds of information-related terminals is expanding continuously, as in the increase in sales of mobile appliances such as a mobile phone, a digital camera, and a PDA and a large-type image display apparatus such as a liquid crystal television. A transparent substrate for displaying information such as images and characters or inputting information with a touch panel display is mounted on such information-related terminals, and the substrate adopts glass as a material so as to realize high environment performance and ensure high reliability.
Various environment performances required for glass used for the application shouldering the prosperity of the information industry include various physicochemical performances such as mechanical strength in conformity with the environment in which glass is used, chemical resistance such as weather resistance, and appropriate optical constants such as a transmittance and a refractive index. Therefore, designing a glass material determines an ultimate composition for solving all those problems. A secondary treatment has been conducted with respect to glass so as to solve the higher problems, which cannot be solved only by designing a glass material. Examples of the secondary treatment include physical reinforcement such as the adjustment of a refractive index and a density, a slow cooling operation (which is also called annealing) for maintaining strength, air-cooling reinforcement for reinforcing a glass surface, and chemical reinforcement such as ion exchange.
Of the secondary treatments, the chemical reinforcement of a glass surface has been utilized for a glass product used for various applications requiring reinforcement. Glass products to be chemically reinforced cover a fairly broad spectrum, which includes small things such as a cover glass for a watch such as a wristwatch to large things such as a window plate glass. Further, a large number of inventions have been carried out, which overcome weak points caused when a chemical reinforcement method is conducted. For example, regarding a problem in that the chemical reinforcement method generally decreases the chemical durability of a glass surface, JP 07-223845 A discloses a method of soaking a float plate glass in a potassium nitrate molten salt and further soaking the glass in a lithium aqueous solution so as to produce a chemically reinforced glass excellent in chemical durability. Further, regarding a problem in that a plate glass used for the application such as a touch panel is warped by chemical reinforcement, JP 2004-189562 A discloses an invention which solves the problem by changing the support position of the plate glass while being soaked in a vertical direction for chemical reinforcement with the ratio between the length of a long side and the length of a short side of the plate glass. Further, regarding a problem in that, for chemically reinforcing the entire plate glass, the management of a heat treatment step should be conducted strictly, particularly for treating a large-size plate glass such as a display, which makes it difficult to shorten the time for the step, JP 2006-282492 A discloses an invention solving the problem by spraying an atomized reinforcing agent or a powdery reinforcing agent to a cut portion of a glass plate and irradiating the cut portion with light for heating. Further, JP 2003-514758 A discloses an invention in which a partial reinforcement treatment of a glass plate used for a large display such as a plasma display can be achieved by laminating a paste containing a potassium salt and a high-melting point compound on a glass surface.